This invention relates to new coating compositions and, particularly, to a new binder system for use with highly-filled, particle-bearing coatings wherein it is desired to achieve abrasion resistance without excessive brittleness and loss of flexibility, particularly on repeated creasing.
The following summary of the background is necessarily made with hindsight of Applicant's invention. The publications were discovered using full-text computerized searching methods and Applicant emphasizes that one skilled in the pertinent art of making highly-filled coating systems would not have discovered some such publications in the art except by use of full-text searching techniques which assured mere combinations of key words relating to Applicant's invention would turn up references from non-analogous technical areas. One example of such non-analogous art is U.S. Pat. No. 3,912,511 which discloses an unfilled, ultra-thin (2-micron and no more than 5 micron) film of a polyester/polyurethane/vinylidenechloride-acrylonitrile copolymer blend. That ultra-thin film, of resin only, was utilized unfilled to protect a metal-cylinder against abrasion, and does not address problems associated with of highly-filled, particulate-bearing compositions of the type used on flexible substrates wherein the particles themselves are often several microns or more in maximum dimension.
U.S. Pat. Nos. 4,131,717 and 4,425,263 disclose the use of speciality aromatic polyester polymers as binders for use in highly-filled coating systems. The former patent relates to magnetic tape; the latter patent relates to silver-filled conductive coatings.
A great deal of other work has been done by various inventors attempting to provide binder systems which would provide highly-filled compositions with an improved combination of such properties as adhesion of the coating to flexible resinous substrates, abrasion resistance of the coating, toughness (the area under the pertinent portion of a stress/strain curve of a given coating system) abrasion resistance, and flexibility. Improvements in such systems were to be welcomed in a variety of applications where the physical properties of coatings were limiting the use, and the abuse, which could be tolerated by such products as electrically conductive compositions used as conductors in membrane switches, magnetic coatings on floppy disk recording media, and the like. However, even the best of earlier systems generally required use of such expensive and troublesome solvents as dimethylformamide, tetrahydrofuran or the like.